Semiconductor Nanostructures and Quantum Systems

Research Field

Our group explores a wide range of topics related to the fundamental physics of nanostructured materials and their quantum-electronic and -photonic properties. We study the unique electronic, photonic and quantum properties of materials patterned over nanometer lengthscales and explore how sub-components can be integrated together to realise entirely new materials with emergent properties. This convergence of materials-nanotechnology, quantum electronics and photonics is strongly interdisciplinary, spanning topics across the physical sciences, as well as materials science and engineering.

Offers for Theses in the Group

Quantum Emitters in 2D Materials

2D materials were shown in 2015 to host randomly occurring single-photon emitting sites. Due to unique properties, such as ultimate proximity of the light sources to the surface that result in high photon extraction efficiencies, nuclear spin-free isotopes, valley pseudospin and potential for scalability, 2D materials are extremely promising as building blocks for solid-state photon-based quantum information. They have the potential to overcome the limitations of the current systems as highly sensitive, easily integrable quantum light sources and qubits of the future1. However, in current 2D quantum emitters the photon emission energy is random2. This prevents photon indistinguishability, a non- negotiable requirement for both fundamental studies and applications. Moreover, the current fabrication process is incompatible with silicon photonics and on-chip integration. To unleash the full impact of 2D materials on quantum science and technology, we are currently attempting a novel fabrication strategy. In the first part of the project, you will realize quantum dots of 2D semiconductors top-down, with dimensions below those achievable through conventional lithography systems, using a combination of etching masks made of colloidal quantum dots and by Helium Ion Beam Lithography followed by Reactive Ion Etching. Such quantum dots will be deterministic, scalable and will overcome the critical limitations of the current solid-state quantum emitters in 2D materials. You will study the optical properties of such quantum emitters at cryogenic temperatures and in the presence of magnetic fields. Further, you will have the option of integrating such quantum emitters and their arrays with optical cavities and waveguides, realizing spin-qubits registers made of arrays of independently charged quantum-dots and studying the effect of interactions among separate quantum emitters placed at a subwavelength distance. This is a challenging but no current solid-state quantum dot system satisfies the requirements to do so.

Some experience in the areas of optics, electronics, programming or cleanroom fabrication will be beneficial, but secondary to your personal motivation and commitment to this fascinating project. You will gain skills and knowledge and probably become an expert in various scientific research tasks, including but not limited to nanoscale cleanroom fabrication and state-of-the-art electro-optical measurements at cryogenic temperatures.

You should: be a highly motivated student with a curious and open mind looking to solve. This is a challenging but potentially ground-breaking project in the framework of quantum science and technology. You will work in close collaboration with a small team of Ph.D students and a postdoc, therefore teamwork is crucial. You must enjoy working with others, have a knack for a good laugh and you shouldn’t take yourself too seriously, these skills will help with the regular frustrations arising when doing research.

You will get: experience on state-of-the-art (or beyond) nanofabrication and on performing optical spectroscopy in state-of-the-art laboratories, a sound understanding of the physics of 2D materials and solid-state quantum optical systems, and if everything goes well a nice (or even amazing) paper in a top journal. Maybe most importantly, you will also have a lot of fun along the way.

As we expect a significant number of applicants, please enquire as soon as possible. The final decision will take place until the 1st of May. For inquiries feel free to write to Dr. Matteo Barbone: Matteo.Barbone@wsi.tum.de

Wavelength-scale coherent optical sources are vital for a wide range of applications in nanophotonics ranging from metrology and sensing to nonlinear frequency generationand optical switching. Since precision metrology and spectroscopy is enabled by the ability to generate phase-stabilized trains of ultrafast laser pulses, it is of particular interest to realize such a technology on-chip. However, the complexity of conventional mode-locked laser systems has so far hindered their realization at the nanoscale. Recently, we demonstrated that subsequently emitted ultrafast laser pulses emitted from incoherently pumped GaAs-AlGaAs core-shell nanowire lasers remain mutually phase coherent over timescales that are approximately ten times longer than the emitted pulse duration1. A deeper understanding of the factors governing the electron and photon dynamics of NW lasers is now crucial for further developments.

In this project, you will, therefore, investigate the carrier relaxation and gain dynamics of novel quantum confined nanowire laser structures by employing ultrafast pump-probe spectroscopy. Thereby you will explore the influence of composition modulation and low dimensional gain media on the frequency and phase-dependent lasing characteristics. Further, you will have the option of extending the current pump-probe setup in order to study coupling and switching phenomena in NW-based silicon photonic circuits.

You will get experience in performing state-of-the-art ultrafast spectroscopy at room and cryogenic temperatures, and a solid understanding of the physics of semiconductor nanolasers.

In this thesis, you will be closely working with several other student members at WSI. Good knowledge in physics, especially optics, semiconductors, as well as previous experience with lab work related to of nanophotonics or quantum optics are a benefit, but secondary to motivation and commitment. Applications should be sent to Andreas.Thurn@wsi.tum.de, Gregor.Koblmueller@wsi.tum.de, or Jonathan.Finley@wsi.tum.de. Please include your CV, a copy of your Bachelor Thesis and a transcript of your grades (Bachelor & Master).

Our lab is using solid state qubits to build sensors, for instance for magnetic fields. We aim to apply them to various applications, with a particular focus on life sciences.

We are seeking a MSc student to study a novel application, imaging of electric action potentials of neurons, the cells performing computation in the brain. This should involve the development of a new type of sensor, based on solid state quantum materials, smart signal processing by artificial neural networks, or a combination of both.

Techniques:

* You will learn to prepare microscopy samples of both solid state samples and cell cultures.

* You will design an experiment to detect the weak optical signals from these samples in one of our existing microscope setups. This will involve development of advanced optics and control software.